Al Qaeda leader Ayman al-Zawahiri called for the ouster of Syria's "pernicious, cancerous regime," raising fears that Islamist militants will try to exploit an uprising against President Bashar Assad that began with peaceful calls for democratic change but is morphing into a bloody, armed insurgency.

The regime has long blamed terrorists for the 11-month-old revolt, and Zawahiri's endorsement creates new difficulties for the US, its Western allies and Arab states trying to figure out a way to help force Assad from power. On Sunday, the 22-nation Arab League called for the UN. Security Council to create a joint peacekeeping force for Syria, but Damascus rejected it immediately.

In an eight-minute video message released late Saturday, Zawahri called on Muslims to support Syrian rebels.

"Wounded Syria is still bleeding day after day, and the butcher (Assad) isn't deterred and doesn't stop," said Zawahri, who took over Al Qaeda after Osama bin Laden was killed by US special forces in Pakistan last May. "However, the resistance of our people in Syria is escalating and growing despite all the pains, sacrifices and blood."

The United Nations estimates more than 5,400 people have been killed in Syria since the uprising began in March. But that figure is from January, when the UN stopped counting because it couldn't gather reliable data there anymore.

While many of the anti-government protests sweeping the country remain peaceful, the uprising as a whole has become more violent in recent months as frustrated demonstrators and army defectors take up arms to protect themselves from a steady military assault. An increasing number of army defectors known as the Free Syrian Army have launched attacks, killing soldiers and security forces.

Syria now has become one of the deadliest conflicts amid the uprisings in the region that began early last year, and many fear the country of 22 million at the heart of the Arab world is on the verge of a civil war that could spread to neighbors.

A string of suicide attacks have killed dozens of people since late December. The latest, twin bombings in the major northern city of Aleppo, killed at least 28 people on Friday, the government said. Some 70 people were killed in earlier attacks in the capital, Damascus, on Dec. 23 and Jan. 6. All the blasts struck security targets.

Is it Al Qaeda?

No one has taken responsibility for the attacks, but the regime immediately blamed Al Qaeda.

Saturday's statement by Zawahri appears to bolster Assad's accusations, but the Syrian opposition and the Free Syrian Army reject the government's claims entirely. They accuse forces loyal to the regime of setting off the blasts to smear the opposition, terrify people into submission and exploit fears of chaos and sectarian warfare.

For many Syrians, the uncertainty over the future is cause for alarm in a country that has watched neighboring Lebanon and Iraq descend into bloody wars over the years. Syria is a fragile jigsaw puzzle of Middle Eastern backgrounds including Sunnis, Shiites, Alawites, Christians, Kurds, Druse, Circassians, Armenians and more.

After Friday's bombings in Aleppo, Zuheir al-Atasi, a member of the opposition Syrian National Council, accused the government of staging the attacks.

"After the heavy explosions, members of the opposition went to the site to film it. There were ambulances but no corpses. We documented that on tape," he said in Vienna during a gathering of Syrian opposition groups. "When the Syrian National TV arrived they started to bring out corpses. Once again we witnessed a theater play."

There is virtually no way to determine who was behind the attacks or to perform an independent investigation in Syria, one of the most authoritarian states in the Middle East. Assad has largely sealed off the country and prevented reporters from moving freely. The Arab League sent a now-suspended observer mission into the country to provide an outside view, but government minders accompanied the team.

The dangers of chaos

Salman Shaikh, director of the Brookings Doha Center, a think tank in the Qatari capital, said prolonged chaos in Syria could open the door to militant groups like Al Qaeda.

"The longer this goes on, we may get a more permissive environment in Syria for these kinds of characters as the Syrian people get more and more desperate," he said. "I don't think they would be welcomed in Syria but there may be desperate people in Syria who are looking for any kind of help."

Still, Shaikh is not convinced that Saturday's statement was anything more than the terrorist group trying to reassert its influence in the Middle East, now that the Arab Spring uprisings have, in many ways, pushed it to the sidelines.

"Al-Zawahri's pronouncement, to me, is a propaganda effort that says, 'We're alive and well in the Mideast,'" he said.

He acknowledged that the suggestion that Al Qaeda could become involved in the uprising could have a "chilling effect" on efforts by the West to stem the bloodshed.

"Certainly the US policymakers are advised by their last experience and their last experience is Iraq. So yes, I presume there would be alarm and hesitation in getting further involved," he said.

In Saturday's Internet posting, Zawahri asked Muslims in Iraq, Jordan, Lebanon and Turkey to join the uprising against Assad's regime, saying Syrian rebels must not rely on the West. Syria was the third largest supplier of foreign fighters during the height of the Sunni insurgency in Iraq, after Saudi Arabia and Libya.

"Don't depend on the West and Turkey, which had deals, mutual understanding and sharing with this regime for decades and only began to abandon it after they saw it faltering," Zawahiri said. "Instead, depend on Allah alone and then on your sacrifices, resistance, and steadfastness."

He urged Syrians to oppose help from the Arab League and "its corrupt agent governments."

Hours later, a Sunni sheik in Iraq's northern Kurdish region said a group of clerics in the area is calling for a jihad, or holy war, against Assad's regime.

"Jihad is the duty of every Muslim against the Assad regime," said Sheik Abdul-Rahman Abdul-Karim Barzanji, describing the edict issued by the Union of the Scholars of Islam in Kurdistan. "Any support from any Muslim or country is forbidden."

Arab League

Syria has a large population of Kurds, who have mostly stayed on the sidelines of the uprising since Assad's regime began giving them long-denied citizenship as a gesture to win support.

The Arab League has been trying to end the bloodshed in Syria.

On Sunday, the Arab League called for the UN Security Council to create a joint peacekeeping force for Syria. The resolution adopted by the League also demanded that Syrian regime forces lift the siege on neighborhoods and villages and pull troops and their heavy weapons back to barracks.

The central city of Homs has seen some of the worst violence of the uprising, and activists said regime forces were shelling rebellious neighborhoods on Sunday. Hundreds are believed to have been killed since the latest assault in Homs began more than a week ago.

The Arab League resolution also calls on Syrian opposition groups to unite ahead of a Feb. 24 meeting of the "Friends of Syria" group," which includes the United States, its European allies and Arab nations working to end the conflict.

Syria's ambassador to Egypt, Ahmed Youssef, swiftly rejected the resolution, saying it showed the collective Arab will has been "hijacked" by states led by Saudi Arabia and Qatar, which are opposed to Assad's regime.

Syria's ambassador to the Arab League, Ahmed Youssef, was quoted in Syria's state media as saying that Qatar and Saudi Arabia were "living in a state of hysteria after their last failure at the U.N. Security Council to call for outside interference in Syria's affairs and impose sanctions on the Syrian people."

The regime's crackdown has left it almost completely isolated internationally, except for key support from Russia and China, which delivered a double veto to block a U.N. resolution calling on Assad to leave power.

Moscow's stance is motivated in part by its strategic and defense ties, including weapons sales, with Syria. Russia also rejects what it sees as a world order dominated by the U.S. Last month, Russia reportedly signed a $550 million deal to sell combat jets to Syria.

The veto prompted Western and Arab countries to consider forming a coalition to help Syria's opposition, though so far there is no sign they intend to give direct aid to the Free Syrian Army.